Long-Term debt and Equity Financings (Narrative) (Details)	6 Months Ended
Jun. 30, 2017 USD ($)
Union Electric Company \| Senior Secured Notes, 2.95%, Due 2027 - $400 Issuance \| Secured Debt
Long-Term Debt And Equity Financings [Line Items]
Total principal amount of notes	$ 400,000,000
State interest rate	2.95%
Proceeds from issuance of secured debt	$ 396,000,000
Union Electric Company \| Senior Secured Notes640 Due2017
Long-Term Debt And Equity Financings [Line Items]
State interest rate	6.40%
Repayments of other long-term debt	$ 425,000,000
Ameren Transmission Company of Illinois
Long-Term Debt And Equity Financings [Line Items]
Redemption price, percentage	100.00%
Ameren Transmission Company of Illinois \| Senior Unsecured Notes, 3.43%, Due 2050 \| Unsecured Debt
Long-Term Debt And Equity Financings [Line Items]
Total principal amount of notes	$ 300,000,000
State interest rate	3.43%
Proceeds from issuance of secured debt	$ 149,000,000
Ratio of indebtedness to net capital	0.70
Ratio of indebtedness to total assets	0.10
Maximum \| Ameren Transmission Company of Illinois \| Senior Unsecured Notes, 3.43%, Due 2050 \| Unsecured Debt
Long-Term Debt And Equity Financings [Line Items]
Total principal amount of notes	$ 450,000,000
Minimum \| Ameren Transmission Company of Illinois
Long-Term Debt And Equity Financings [Line Items]
Redemption price, percentage	5.00%
Minimum \| Ameren Transmission Company of Illinois \| Senior Unsecured Notes, 3.43%, Due 2050 \| Unsecured Debt
Long-Term Debt And Equity Financings [Line Items]
Total principal amount of notes	$ 150,000,000

Long-Term Debt And Equity Financings [Line Items]

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Indebtedness divided by total assets.

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Face (par) amount of debt instrument at time of issuance.

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Contractual interest rate for funds borrowed, under the debt agreement.

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The cash inflow from amounts received from issuance of long-term debt that is wholly or partially secured by collateral. Excludes proceeds from tax exempt secured debt.

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Indebtedness divided by net capital.

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Amount of cash outflow for the payment of debt classified as other, maturing after one year or the operating cycle, if longer.

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